Method of operating a heated guide vane assembly

ABSTRACT

A method of operating a heated guide vane assembly for turbomachinery, the heated guide vane assembly including a plurality of guide vanes each having two major surfaces joined about their periphery by edges and an associated electric heater element secured to at least one major surface of the guide vanes. The method includes the steps of energizing heater elements on at least one of the guide vanes, de-energizing heater elements on at least one of the guide vanes, and energizing heater elements on at least one of the guide vanes which was not energized in the first energizing step.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

The US Government may have certain rights in this invention pursuant toContract No. SFX awarded by the US Department of the Air Force.

BACKGROUND OF THE INVENTION

The technology described herein relates generally to turbomachinery,particularly to gas turbine engines, and more particularly, to a methodof operating a heated guide vane assembly for gas turbine engines.

Many gas turbine engine assemblies include a fan assembly that ismounted upstream from a core gas turbine engine. During operation, aportion of the airflow discharged from the fan assembly is channeleddownstream to the core gas turbine engine wherein the airflow is furthercompressed. The compressed airflow is then channeled into a combustor,mixed with fuel, and ignited to generate hot combustion gases. Thecombustion gases are then channeled to a turbine, which extracts energyfrom the combustion gases for powering the compressor, as well asproducing useful work to propel an aircraft in flight. The other portionof the airflow discharged from the fan assembly exits the engine througha fan stream nozzle.

To facilitate channeling the airflow into the fan assembly, some knowngas turbine engine assemblies includes an inlet guide vane assembly thatis used to direct the air in a desirable orientation toward the fanblades. Inlet guide vanes (IVGs) may be provided in either a fixedorientation or may be constructed in a variable inlet guide vaneconfiguration. Variable inlet guide vanes (VIGVs) may be adjusted forvarious operating conditions and environments, often by pivoting theguide vanes about an axis, to achieve the desired airflowcharacteristics leading into the fan assembly. In addition to turningthe fan airflow, the inlet guide vane assembly may also providestructural stiffness to the fan frame. More specifically, inlet guidevane assemblies generally include a plurality of inlet guide vanes thatare coupled to the fan frame.

Inlet guide vane assemblies, along with other structural elements ofaircraft and aircraft engines, may be susceptible of forming iceaccumulation under certain operating and environmental conditions. Iceaccumulation on such structures, besides adding weight to thestructures, often has a detrimental effect on performance throughalteration of the surface texture and structural shape of the elementundergoing ice accumulation.

Various approaches to addressing ice accumulation have been developed,including the use of heated air supplied from a source such as a warmerpressurized source within the engine itself. However, there remains aneed for an improved guide vane heater to effectively and efficientlyaddress ice accumulation.

BRIEF SUMMARY OF THE INVENTION

A method of operating a heated guide vane assembly for turbomachinery,the heated guide vane assembly including a plurality of guide vanes eachhaving two major surfaces joined about their periphery by edges and anassociated electric heater element secured to at least one major surfaceof the guide vanes. The method includes the steps of energizing heaterelements on at least one of the guide vanes, de-energizing heaterelements on at least one of the guide vanes, and energizing heaterelements on at least one of the guide vanes which was not energized inthe first energizing step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional illustration of an exemplary gas turbineengine assembly;

FIG. 2 is an elevational view of an inlet guide vane suitable for use inthe gas turbine engine assembly shown in FIG. 1;

FIG. 3 is an exploded perspective view of the guide vane of FIG. 2illustrating the relationship of the vane to the heater mesh element;

FIG. 4 is a perspective view of the inlet guide vane of FIG. 3;

FIG. 5 is an exploded perspective view of another embodiment of a guidevane suitable for use in the gas turbine engine assembly of FIG. 2; and

FIG. 6 is a perspective view of the inlet guide vane of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross-sectional schematic illustration of an exemplary gasturbine engine assembly 10 having a longitudinal axis 11. Gas turbineengine assembly 10 includes a fan assembly 12 and a core gas turbineengine 13. Core gas turbine engine 13 includes a high pressurecompressor 14, a combustor 16, and a high pressure turbine 18. In theexemplary embodiment, gas turbine engine assembly 10 also includes a lowpressure turbine 20, and a multi-stage booster compressor 22.

Fan assembly 12 includes an array of fan blades 24 extending radiallyoutward from a rotor disk 26. Gas turbine engine assembly 10 has anintake or inlet side 28 and an exhaust side 30. Fan assembly 12, booster22, and turbine 20 are coupled together by a first rotor shaft 31, andcompressor 14 and turbine 18 are coupled together by a second rotorshaft 32.

In operation, air flows through fan assembly 12 and booster 22. Thecompressed air that is discharged from booster 22 is channeled throughcompressor 14 wherein the airflow is further compressed and delivered tocombustor 16. Hot products of combustion (not shown in FIG. 1) fromcombustor 16 are utilized to drive turbines 18 and 20 before beingexhausted through an exhaust duct 42, and turbine 20 is utilized todrive fan assembly 12 and booster 22 by way of shaft 31. Gas turbineengine assembly 10 is operable at a range of operating conditionsbetween design operating conditions and off-design operating conditions.

A plurality of inlet guide vanes 70 that typically extend substantiallyradially, between a radially-outer mounting flange and a radially-innermounting flange, and are circumferentially-spaced around inlet 28, guideincoming airflow 14 into the fan assembly 12. Inlet guide vanes 70 serveto turn the airflow upstream from rotating blades such as fan blades 24for aerodynamic purposes to achieve the desired airflow characteristicsinto and through the fan assembly 12 under various operating conditions.Outlet guide vanes (shown but not numbered in FIG. 1), supportingstruts, and other structures may be provided upstream and/or downstreamof the fan blades 24 for structural or aerodynamic purposes.

FIG. 2 is an elevational view of an inlet guide vane 70 suitable for usein the gas turbine engine 10 of FIG. 1. Guide vane 70 has a leading edge71, a trailing edge 72, an inner edge 73, and an outer edge 74. Guidevane 70, in the embodiment shown, is an airfoil-shaped structure whichhas two major surfaces joined about their periphery by edges 71-74.Guide vane 70 is secured in place by suitable mounting features such asinner and outer mountings 75 and 76, respectively. Mounting featuressuch as inner and outer mountings 75 and 76 may provide for adjustmentof the orientation of guide vane 70 on a one-time or continuous basis,or may maintain it in a fixed position relative to the gas turbineengine 10.

As shown in FIG. 2, the inlet guide vane 70 also includes a heaterelement 80 mounted on a major surface thereof. Heater element 80 iselectrically powered and is connected to a suitable electrical powersource through suitable electrical connections (not shown forillustrative clarity). The heater element 80 converts electrical energyinto heat energy, which may then be transferred to accumulated iceoverlying the heater element or adjoining surfaces of the inlet guidevane 70 which receive heat from the heater element 80.

FIG. 3 shows in greater detail the relationship of heater element 80 toinlet guide vane 70. To accommodate the installation of heater element80, the inlet guide vane 70 includes a recess 77 suitably sized andshaped to receive the heater element 80 while maintaining the desiredaerodynamic profile of inlet guide vane 70. To permit a substantiallyflush installation, where the heater element 80 is substantially flushwith the outer surface profile of a major surface of the inlet guidevane 70, the recess is constructed at a depth “d” which correlates to athickness “t” of the heater element 80, plus any additional localized orgeneralized dimension needed for adhesive or other mounting features(not shown) to secure the heater element 80 in place in recess 77. Byway of example, a recess depth of 0.030 inches may be utilized toaccommodate a heater element plus its bonding agent.

Heater element 80 is suitably sized and shaped, and configured todeliver sufficient heating value, to provide the desiredanti-ice-accumulation benefit to inlet guide vane 70 under variousoperating conditions. In the embodiment shown in FIG. 3, the heaterelement 80 covers a substantial portion of one major surface of inletguide vane 70. FIG. 4 illustrates the fully-assembled inlet guide vane70 with the heater element 80 installed.

FIGS. 5 and 6 depict another embodiment of a heated guide vane 70. Inthis embodiment, the heater element 80 takes the form of an elongatedstrip which is sized, shaped, and adapted to be secured to acorrespondingly sized and shaped recess 77 which follows the peripheryof a major surface of the guide vane 70. This configuration focuses theheat generated by the heater element in a specific region of the guidevane 70 rather than heating the entire guide vane generally through acontinuous heater element as in the embodiment of FIGS. 2-4, whichcovers a majority of a major surface of the guide vane 70. As in theprevious embodiment, FIG. 5 illustrates the depth “d” of recess 77 andthe thickness “t” of the heater element 80. The “picture frame” orperipheral configuration concentrates the heat around the periphery ofthe guide vane, namely edges 71-74 shown in FIG. 2. This may result inmore effective distribution of generated heat and hence smaller heaterelement area coverage with reduced power requirements.

FIG. 7 is an elevational view illustrating, looking rearward from thefront of the gas turbine engine, the relationship of the vanes 70 to thereference lines and axes of the gas turbine engine 10. As shown in FIG.3, the guide vanes 70 are circumferentially distributed around thecentral axis 11 of the gas turbine engine 10. Numerical identifiers 1through 6 are used to identify groups of guide vanes 70 which are undercommon control an as to be selectively energized or de-energizedtogether.

In the configuration shown, seventeen guide vanes 70 plus the nose cone15 are included in the control scheme. By way of example, the threeguide vanes identified with the numeral 1 may be energized while theremaining guide vanes 70 and the shaded areas 6 of nose cone 15 arede-energized. The guide vanes 70 identified with the numeral 1 may thenbe de-energized and the guide vanes 70 identified with the numeral 2 mayenergized. In such an exemplary configuration, a pattern of energizingand de-energizing guide vanes 70 may be established to maintain thedesired performance while managing electrical power consumption at alower level than were all guide vanes 70 with comparable power outputssimultaneously energized. In the embodiment shown, sequential sets of 3guide vanes numbered as zones 1 through 5 are energized for their dutycycle and then turned off, then zone 6 with the two remaining guidevanes 70 and the shaded areas 6 of nose cone 15 are energized and thende-energized. The cycle may then be repeated beginning again with zone 1as many times as desired.

Individual guide vanes 70 or groups of guide vanes 70 under commoncontrol may be energized in various patterns or sequences as desired.The respective time periods for energization and de-energization mayalso be determined as necessary to obtain the desired performance. Suchan operating scheme may also be called a “duty cycle” and may bemeasured in terms of time on in comparison with time off and/or in termsof the periodic nature of the cycle (interval between repetitiveevents). An exemplary duty cycle for illustration purposes only may be10 seconds on and 50 seconds off, in which case the energizing timeperiod is shorter than the de-energizing time period for a given heaterelement. In such a configuration, with 6 zones illustrated in FIG. 7,each zone is energized for 10 seconds until all 6 zones have been heatedin turn, after which the cycle repeats itself with the overallperiodicity being 1 minute between successive complete cycles. By sizingall zones to have at least somewhat similar power requirements, asomewhat consistent level of power demand can be obtained.

Other elements may be heated in conjunction or combination with guidevanes 70, such as struts, nose cones, etc., and may be heatedconcurrently or on a different heating scheme. For example, someelements may have a longer duty or heating cycle, or may be set to heatcontinuously, while other elements cycle on and off. In the embodimentshown in FIG. 7, the “X” in the center of the nose cone 15 may remainenergized to serve an anti-icing function (to discourage ice formationin that region) while the other heating zones operate periodically toshed accumulated ice.

The guide vanes 70 may be fabricated from any suitable materials usingany suitable fabrication methods as are known in the art and suitablefor the intended configuration and operating environment. Configurationdetails, such as the number, thickness, and geometry of guide vanes 70,may be determined and implemented to achieve the desired operating andperformance characteristics of the turbomachinery in which they areinstalled. Metallic materials such as Titanium and Titanium alloys maybe utilized, alone or in combination with other non-metallic materials.Guide vanes 70 may be unitarily formed or assembled from individualcomponents, and may be solid elements or may be hollow structures withinterior spaces empty or filled with lightweight materials.

Heater elements 80 may be fabricated from any suitable materials orcomponents as required for the desired heat output and operatingenvironment. Nickel or other conductive materials may be fashioned intoa mesh, grid, or other electrically conductive network and generate heatthrough electrical resistance or other operating modality. The heatoutput and power input may be suitably tailored on apower-per-square-inch basis or other suitable criteria. Power outputdensities of, for example only, 32 W/square inch or 35 W/square inch,may be utilized.

The control system for the heated guide vanes 70 may be located,constructed, and programmed to operate in any manner suitable for theintended physical and operating environment. Additionally, under someoperating conditions it may be desirable to design and operate theheating system to break up and shed ice after some period ofaccumulation (but while still relatively thin and breakable into smallpieces) rather than melting ice and generating liquid water which wouldpass farther through the engine assembly and potentially re-freezelater. Power to operate the heater elements may be provided by a powersource such as a generator, powered by the gas turbine engine associatedwith the heater elements or not so associated, or by any other suitablepower supply.

While much of the discussion has focused on an aviation gas turbineengine as the context for the heated guide vanes, it is foreseeable thatsuch heater installations may be suitable for use in other environmentswherein a guide vane associated with rotating turbomachinery, such aswind or steam turbines.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method of operating a heated guide vane assembly forturbomachinery, said heated guide vane assembly including a plurality ofguide vanes each having two major surfaces joined about their peripheryby edges and an associated electric heater element secured to at leastone major surface thereof, said method comprising the steps of:energizing heater elements on at least one of said guide vanes;de-energizing heater elements on at least one of said guide vanes; andenergizing heater elements on at least one of said guide vanes which wasnot energized in said first energizing step.
 2. A method of operating aheated guide vane assembly for turbomachinery in accordance with claim1, wherein each of said energizing steps includes energizing multipleheater elements.
 3. A method of operating a heated guide vane assemblyfor turbomachinery in accordance with claim 2, wherein said multipleheater elements are secured to multiple guide vanes.
 4. A method ofoperating a heated guide vane assembly for turbomachinery in accordancewith claim 1, wherein said energizing and de-energizing steps arerepeated on a continuous basis.
 5. A method of operating a heated guidevane assembly for turbomachinery in accordance with claim 1, whereinsaid energizing steps are sustained for a shorter time period than saidde-energizing steps for a specific heater element.
 6. A method ofoperating a heated guide vane assembly for turbomachinery in accordancewith claim 1, further comprising a step of energizing a heater elementon another structure.
 7. A method of operating a heated guide vaneassembly for turbomachinery in accordance with claim 1, wherein eachenergizing step has similar power requirements.
 8. A method of operatinga heated guide vane assembly for turbomachinery in accordance with claim1, said assembly further including a control system to selectivelyenergize and de-energize said heater elements.
 9. A method of operatinga heated guide vane assembly for turbomachinery in accordance with claim8, wherein said control system is operable to selectively energize aplurality of heater elements symmetrically arranged around a centerlineof said turbomachinery and selectively de-energize said plurality ofheater elements sequentially in a pattern which advances around saidcenterline.
 10. A method of operating a heated guide vane assembly for agas turbine engine, said heated guide vane assembly including aplurality of guide vanes each having two major surfaces joined abouttheir periphery by edges and an associated electric heater elementsecured to at least one major surface thereof, said method comprisingthe steps of: energizing heater elements on a plurality of said guidevanes; de-energizing heater elements on said plurality said guide vanes;energizing heater elements on a plurality of said guide vanes which wasnot energized in said first energizing step; and repeating saidenergizing and de-energizing steps on a continuous basis.